As a polymer produced by using a diamine as a monomer, a condensation polymer such as a polyamide, a polyamic acid, a polyimide, a polyamic acid ester, a polyamide imide or a polyetherimide has been known. Such a condensation polymer has been used as various electronic materials, and it may be used for a wide range of applications, for example, for a liquid crystal alignment film, an optical film, an adhesive film for a semiconductor, an interlayer dielectric film, etc.
It has been known that an excellent liquid crystal alignment film can be obtained from a functional polymer having amino groups introduced to a main chain or side chains of such a condensation polymer. When using such a liquid crystal alignment film, scars on the film surface and peeling of the film which are problematic at the time of so-called rubbing treatment such that the surface of the film is rubbed with a cloth made of e.g. rayon with pressure, can be suppressed, and further, it is possible to prepare a liquid crystal display device which has a high voltage retention, which has a low ion density and which is excellent in the reliability (Patent Document 1).
Further, it has been known that with such a liquid crystal alignment film, a residual image of a photo-alignment type liquid crystal display device can be reduced (Patent Document 2).
Further, it has been known that if highly basic NH groups are present in the skeleton of a functional polymer constituting a liquid crystal alignment film, solubility of such a polymer in a polymer solution decreases, thus leading to gelation and decrease in storage stability. It has been known that such problems can be solved by substituting the NH groups with a thermally-leaving protecting group (Patent Documents 1 and 3).